Our invention relates generally to automotive transmissions of the type disclosed in U.S. Pat. Nos. 3,393,585; 3,613,484; 3,706,240; 3,714,836; U.S. Ser. No. 24,500 filed Mar. 11, 1987 and U.S. Ser. No. 927,624 filed Nov. 6, 1984. All of these applications and patents are assigned to the assignee of this invention.
An inlet port of a manual timing valve is pressurized from a source of regulated line pressure through a manual valve when the vehicle operator selects certain gears manually. Hydraulic flow through this port enters the manual timing valve through an orifice sized to control the flow rate. A first volume of the timing valve increases in size as a first piston moves due to pressure of fluid flowing to the valve through the orifice. Pressure within the first volume is maintained constant while the first volume expands during a first interval, which ends when the first piston reaches the extremity of its motion. Thereafter, pressure entering the valve through the orifice increases abruptly and causes a second piston to move against the force of a spring due to the increased pressure force developed on the second piston after the first volume stops expanding. As the second piston moves the size of a second volume increases during a second interval until the second piston bottoms. When this occurs, the valve opens a connection between the first port and an outlet port through a bypass line in which there is no restriction.
The system for controlling the timing valve includes two solenoid-operated valves for producing high and low fluid pressures states. The outlet port of the timing valve is connected to a shift valve, which directs the delayed pressure produced by the manual timing valve to a first shift valve. The pressure states of the first solenoid-operated control valve cause the first shift valve to direct the delayed pressure to an intermediate servo, by means of which an intermediate brake band is applied, or to a low/reverse brake in accordance with the gear that is selected manually and the states of the control valves. The delayed pressure directed to the intermediate servo assures that an intermediate band is applied after an intermediate brake. The brake has a higher torque capacity than the band. This assures that when full engine torque is transmitted through the transmission it is carried by the higher torque capacity friction brake but only coasting torque is carried by the lower torque capacity band.